A modified genetic algorithm (MGA) optimization procedure, alongside time series machine learning (ML) classifiers, is proposed to minimize handovers in a digital twin-based visible light communication (VLC) system. Frequent handovers have a direct impact on the overall performance of the VLC system due to the inherent connection downtime of a handover process. The handover scheme proposed in this article considers the receiver trajectory information to minimize handovers, maintaining the system performance below the forward error correction limit. Simulation results indicate that the proposed scheme outperforms a power-based handover scheme, achieving handover reductions of 42.47%. Therefore, the MGA combined to the ML models approach is an effective means of minimizing handovers, as well as improving overall VLC system performance.
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The transmission of constant-envelope orthogonal frequency division multiplexing (CE-OFDM) signals, based on electrical phase modulation, was shown to improve the tolerance to noise and the nonlinearity introduced by light-emitting diodes (LEDs) in visible light communication (VLC) systems. This allows the application of larger signal amplitudes despite the LED-nonlinearities and, thus, data transmission over larger distances. The performance of a 9.51 Mb/s CE-OFDM based system, with 16-QAM subcarrier mapping in a bandwidth of 5 MHz, was compared to the efficiency of a conventional OFDM system. The error vector magnitude (EVM) was reduced from 17.5% to 10% (which is below the FEC limit), an improvement around 43%, when the CE-OFDM scheme was applied in the VLC link of 6 m. A good performance was achieved by the CE-OFDM based VLC system in a link of 8 m, when 4-QAM was used as subcarrier mapping.
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The performance of a visible light communication (VLC) system based on power domain non-orthogonal multiple access (PD-NOMA) is experimentally evaluated in this paper. The simplicity of the adopted non-orthogonal scheme is provided by the fixed power allocation method at the transmitter and the single one-tap equalization executed before the successive interference cancellation at the receiver. The experimental results proved the successful transmission of the PD-NOMA scheme with three users in VLC links of up to 2.5 m, after a proper choice of the optical modulation index. All users achieved error-vector magnitude (EVM) performances below FEC limits in all evaluated transmission distances. At 2.5 m, the user with the best performance reaches an EVM = 2.3 %.
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This study presents a methodology designed to optimize various parameters of each access point within a Multiple-Input Single-Output (MISO) Visible Light Communication (VLC) system. The primary objective is to enhance both power and spectral efficiencies. A MISO-VLC model is presented based on experimental evaluations and a problem formulation considering intermodulation distortions based on Orthogonal Frequency Division Multiplexing modulation. A Hybrid Multi-Objective Optimization (HMO) approach is proposed, combining the Non-Sorting Genetic Algorithm III (NSGA-III) and the Multi-objective Grey Wolf Optimization (MOGWO). The proposed HMO's success was validated by a 66 % reduction in transmitted power, maintaining the Error Vector Magnitude (EVM) performance metrics even at lower power transmission levels and minimizing the guard band to its lower bound.
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Light therapy for older persons with dementia is often administered with light boxes, even though indoor ambient light may more comfortably support the diverse lighting needs of this population. Our objective is to investigate the influence of indoor daylight and lighting on the health of older adults with dementia living in long-term care facilities. A systematic literature search was performed within PubMed, CINAHL, PsycINFO, Web of Science and Scopus databases. The included articles (n=37) were published from 1991 to 2020. These articles researched the influence of existing and changed indoor light conditions on health and resulted in seven categories of health outcomes. Although no conclusive evidence was found to support the ability of indoor light to decrease challenging behaviors or improve circadian rhythms, findings of two studies indicate that exposure to (very) cool light of moderate intensity diminished agitation. Promising effects of indoor light were to reduce depressive symptoms and facilitate spatial orientation. Furthermore, there were indications that indoor light improved one’s quality of life. Despite interventions with dynamic lighting having yielded little evidence of its efficacy, its potential has been insufficiently researched among this study population. This review provides a clear and comprehensive description of the impact of diverse indoor light conditions on the health of older adults with dementia living in long-term care facilities. Variation was seen in terms of research methods, (the description of) light conditions, and participants’ characteristics (types and severity of dementia), thus confounding the reliability of the findings. The authors recommend further research to corroborate the beneficial effects of indoor light on depression and to clarify its role in supporting everyday activities of this population. An implication for practice in long-term care facilities is raising the awareness of the increased lighting needs of aged residents. Original article at: https://doi.org/10.2147/CIA.S297865
MULTIFILE
The nonlinearity induced by light-emitting diodes in visible light communication (VLC) systems presents a challenge to the parametrization of orthogonal frequency division multiplexing (OFDM). The goal of the multi-objective optimization problem presented in this study is to maximize the transmitted power (superimposed LED bias-current and signal amplification) for both conventional and constant envelope (CE) OFDM while also maximizing spectral efficiency. The bit error rate (BER) metric is used to evaluate the optimization using the non-dominated sorting genetic algorithm II. Simulation results show that for a BER of 1×10 −3 , the signal-to-noise ratio (SNR) required decreases with the guard band due to intermodulation distortions. In contrast to SNR values of approximately 13 and 25 dB achieved by traditional OFDM-based systems, the VLC system with CE signals achieves a guard band of 6% of the signal bandwidth with required SNR values of approximately 10.8 and 24 dB for 4-quadrature amplitude modulation (QAM) and 16-QAM modulation orders, respectively.
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Background The experiences of residents who have communication difficulties such as dysphasia are largely absent from the literature. Aim To illuminate the everyday experiences of four residents with severe communication difficulties living in a residential care setting in the Netherlands. Methodology & Methods A collective case study methodology was used. Seventy-five hours of observation, interview and documentary data was gathered over six weeks. Alternative strategies of communication were developed to enable the co-creation of dialogue between participants and researcher. For example, a participant who could not talk used intentionally created artwork to share her ideas with the researcher. Findings Participants' daily experiences were characterised by struggling against the constraints of the residential setting: having to wait, having unmet needs, experiencing vulnerability and uncertainty. Participants' communication difficulties exacerbated these constraints. Their experiences of struggling were sometimes ameliorated by significant social contact with family or particular staff members, and engaging in enjoyable activities. Occasionally the experiences of enjoying the here-and-now, and being 'seen' as a person by the other, would create beautiful moments in which truly person centred engagement would occur. These moments were neither articulated nor recorded, and were thus invisible after they had occurred. Similarly, the experiences of struggling against the constraints were neither acknowledged nor recorded. Significant experiences in the lives of these four residents were therefore invisible to others. The unifying theme representing the participants' daily experiences was: That which goes unsaid. Discussion It was necessary to develop communication strategies which would by-pass the researcher's assumptions and enable participants to introduce their own ideas and opinions. This ongoing process of co-creation of dialogue required work from, and trust between, participants and researcher. What is new? Expressly seeking the views of residents with communication difficulties Successfully using process consent with participants in this situation Using intentionally created artwork during data gathering in this context What has regional, national or international relevance? The findings indicate that people with communication difficulties may not receive optimal care in residential settings in the Netherlands. Methods are described which could be used by practitioners in their everyday work, and which show facilitators or practice developers how they can help carers to engage in more effective communication with this kind of resident. Additionally, this research contributes to the international discussion about ethical participation of vulnerable people in research.
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In this paper I describe the ways in which the communication discipline can make a hidden crisis transparent. For this purpose I examine the concept of crisis entrepreneurship from a communication point of view. Using discourse analysis, I analyse the discursive practices of crisis entrepreneurs in the domain of education in the Netherlands. This paper is part of my Ph.D. project in which I examine the dilemmas encountered by crisis entrepreneurs and the interactional solutions they choose in addressing a crisis. In my Ph.D. project I have analysed how crisis entrepreneurs use discursive practices: (1) to show the factuality of the problem. For example, the way the problem is presented is too theoretical and is not a problem in reality; (2) to present the credibility of the messenger as an authentic, legitimate spokesman. Crisis entrepreneurs may be accused of wanting to attract attention to their own cause; (3) to create the accountability for the problem and the solution. For example, crisis entrepreneurs can be accused of nursing personal grievances or of drawing attention to the issue without actively attempting to solve it. The conclusion is that a communication professional is able to recognize a problem raised by crisis entrepreneurs. Knowledge of interactional dilemmas helps communication professionals understand the potential of crisis entrepreneurs.
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I will examine the ways in which a hidden crisis can be exposed from a communications point of view. Therefore, this examination of the concept of crisis entrepreneurship is also relevant tot communication professionals. The article is in the form of proto-research and will shed light on the dilemmas experienced by crisis entrepreneurs and the interactional solutions they apply to cope with such dilemmas
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